1. Field of the Invention
The present invention relates to a solder material useful for bonding of various metallic members such as electronic parts, mechanical parts and the like, and to a manufacturing method thereof. More particularly, the present invention relates to a solder material containing no lead and enabling to form a suitable bond in joining of metallic members, and to a manufacturing method thereof.
2. Related Art
Soldering is an art for bonding a substance by using a substance having a low melting point, and has been used since old times. It is generally said that the origin of the soldering can be traced up to ancient Mesopotamian civilization. In current industries, soldering is widely used in assembling of mechanical parts and bonding of electronic devices. In regard to the electronic devices, the solder is used for bonding in a mounting process for mounting electronic parts such as semiconductors, microprocessors, memories, resistors and the like to a substrate. Its advantage is not only to fix a part to the substrate, but also to form electrical connection by electric conductivity of the metal contained in the solder. This point is different from organic series adhesive agents.
The solder which is generally used is eutectic solder composed of tin and lead, having a eutectic point of 183xc2x0 C. This is used for bonding sheet materials of aluminum, copper or the like. It is characterized by the eutectic point which is not only lower than the melting point of metallic base material to be soldered, but also lower than a temperature in which gasification of thermosetting resin begins. Further, it has been known than tin component of the eutectic solder forms a particular intermetallic compound on an interface with a copper plate, thereby intensifying bonding strength between the solder and copper. In addition to the eutectic solder composed of tin and lead having such a characeristic, solder composed of tin and zinc, solder composed of silver and tin, etc. have been used on trial. However, their wettabilities are poor, thereby providing a poor connectability. Thus, they have not been used in actual fields.
As described above, bonding by soldering is still important in manufacture of electronic devices. In today""s world in which personal electronic devices such as personal computer, mobile telephone and pager have been spreading quickly, the importance of solder in electronic device mounting technology has been intensified.
Spreading of electronic devices contributes to enrichment of people""s life. However, on the contrary, if a large amount of electronic devices disused are scrapped, there is a fear that wasted electronic devices may pollute the environment. In view of this, recycle of electronic devices and manufacturing without use of harmful substances have been advocated. In particular, removal of harmful substances is desired for prevention of environmental pollution, and it is also required to develop in the art of bonding with solder.
From such a condition, bonding skill by using solder containing no lead has been demanded. However, solder in which lead in substituted with other metal or solder containing a combination of other metals cannot be handled at such a low temperature that bad influence upon the base metal by high temperatures can be avoided, and the wettability is so poor that the solder is not fixed to the base metal satisfactorily. Thus, such a solder can be applied to neither fine soldering treatment such as mounting in semiconductor devices or ordinary bonding by solder. Particularly, solder with tin and zinc has too many problems to be solved, therefore, it is considered impossible to use it for actual application in electronic mounting.
To enable use of solder without lead in fine soldering works such as thick film formation, conductor circuit formation and semiconductor mounting, a screen printing method using solder paste in which solder powder and flux are mixed has been proposed. The flux used in solder paste is generally classified to organic compound, inorganic compound and resin as shown in Japanese Industrial Standard Z3284. In the case when organic compound or resin is used, halogen salt, organic acid salt and the like of organic acid and amino group are frequently added as active ingredient. In the case of inorganic compound, ammonium halide, zinc halide, tin halide, phosphoric acid, hydroacid halide or the like are often added. Since these additives corrode metals, inspection for corrosion due to flux residue after reflowing of solder paste is necessary. Moreover, organic substance evaporating when paste is heated to remove flux, must be treated.
It is therefore the primary object of the present invention to solve the problems in the prior art as described above and to provide a novel solder material which contains metals applicable for wide fields, instead of lead which may cause environmental pollution when a product using such a solder is wasted, and which is suitable for mounting electronic parts on a substrate.
Another object of the present invention is to provide a method of manufacturing d novel solder material, comprising the steps of:
In order to accomplish the above objects, the solder material, according to the present invention, comprises a first layer composed of a first metallic material and a second layer composed of a second metallic material which is different from the first metallic material, the first layer being formed in an elongated shape having axiality, and the second layer covering the first layer to surround the axis of the first layer.
In one aspect of the invention, the first metallic material contains zinc, and the second metallic material does not substantially contain zinc but contains tin.
In the above, wherein the solder material is a substantially binary solder material which contains zinc at a content of approximately 3 to 12% by weight, and wherein the oxygen content of the solder material is 100 ppm or less.
In another aspect, the solder material is in a form of a wire, a granule round or substantially spherical, or a planar form selected from the group consisting of a sheet, a tape and a planar fragment.
In order to accomplish the above objects, the method of manufacturing a solder material, according to the present invention comprises the steps of: covering a first metallic material with a second metallic material which is different from the first metallic material to prepare a covered body; and rolling the covered body to prepare a solder material comprising a first layer formed of the first metallic material in an elongated shape having axiality and a second layer covering the first layer to surround an axis of the first layer.
In one aspect of the invention, the covered body at the rolling step is rolled in such a manner that the covered body is drawn in one direction, thereby the solder material is prepared in a form of a wire in which the first layer has uniaxiality.
In another aspect, the manufacturing method further comprises, after the rolling step, the step of: cutting the solder material in a direction intersecting the axis of the first layer to granulate the solder material.
In the above, it is possible that the solder material at the cutting step is forcingly cut with deformation of the solder material so that the second layer is deformed to substantially completely cover the first layer.
In the above, it is also possible that the manufacturing method further comprises, after the cutting step, the step of: deforming the second layer of the granulated solder material by application of force or heat.
In the above, it is possible that the granulated solder material at the deforming step is deformed round or substantially spherical.
In another aspect, the covered body at the rolling step is rolled in such a manner that the covered body is drawn in two directions, thereby the solder material is prepared in a form of a sheet in which the first layer has biaxiality.
In the above, the manufacturing method may further comprises, after the rolling step, the step of: cutting the solder material in a form of a tape.
In the above, it is possible that the the solder material at the cutting step is forcingly cut with deformation of the solder material so that the second layer is deformed to substantially completely cover the first layer.
In the above, the manufacturing method may alternatively comprises, after the rolling step, the step of: cutting the solder material in a form of a planar fragment.
In the above, it is possible that the solder material at the cutting step is forcingly cut with deformation of the solder material so that the second layer is deformed to substantially completely cover the first layer.
In another aspect, the first metallic material contains zinc, and the second metallic material does not substantially contain zinc but contains tin.
In another aspect, the manufacturing atmosphere is a substantially non-oxidizing atmosphere.